What is an optical transceiver?
A hot-pluggable electro-optical converter that slides into a switch, router or server. Common form factors are SFP (1 G), SFP+ (10 G), SFP28 (25 G), QSFP+ (40 G) and QSFP28 (100 G). The question we answer below is simple: “Which of these can I mix and match without killing the link?
What “compatibility” really means?
All reputable transceivers follow the Multi-Source Agreement (MSA). MSA defines size, pin-out, power and signalling so parts from different makers can physically fit and electrically talk to each other. The remaining variable is vendor ID in the EEPROM—exactly what i7Fiber re-codes before shipment so every module is accepted by the target platform.
SFP vs SFP+
Case A – SFP in an SFP+ port
• Works 99 % of the time.
• Port will lock to 1 G.
• Example: 1000BASE-SX SFP in the SFP+ slot of a 10 G switch talking to a 1000BASE-SX SFP in an older gigabit switch over OM3 MMF.
Case B – SFP+ in an SFP port
• Physically fits, but the port electronics are 1 G only—link will stay down. Use a native 1 G module instead.
Case C – Linking SFP and SFP+ switches
• Over fiber: normally impossible unless the SFP+ side is a dual-rate 1/10 G optic.
• Over copper: 10GBASE-T SFP+ auto-negotiates to 1 G, so you can patch it to a 1000BASE-T SFP with a Cat-6 cable.
SFP28 vs SFP+
SFP28 ports are backward-compatible:
• SFP+ 10 G module in SFP28 port → link at 10 G.
• SFP28 25 G module in SFP+ port → link will not come up.
QSFP28 vs QSFP+
QSFP28 ports are backward-compatible:
• QSFP+ 40 G optic in QSFP28 port → works at 40 G if you set the port speed to 40 G.
• QSFP28 100 G optic in QSFP+ port → not supported.
How i7Fiber removes the guesswork?
• Every module is pre-coded for your exact switch model (Arista, Cisco, Dell, HPE, Juniper, etc.).
• Dual-rate firmware available for 1/10 G and 10/25 G optics.
• In-field re-coding? Use the free i7Fiber Toolbox—USB-C programmer + web portal—to change vendor ID, DDM thresholds or firmware in minutes.
Take-away rules
• Newer ports accept older optics, never the reverse.
• Match speed on both ends; auto-negotiation is rare above 1 G.
• When in doubt, ask i7Fiber for a pre-coded solution—shipped same day, lifetime warranty.
